The present invention relates to an institutional organ of the classical type, and in particular to a mixture generation system for such an organ.
Present-day electronic organs generally fall into three classes: smaller home organs which are voiced to simulate a wide range of modern instruments but are not designed to closely simulate a pipe organ, electronic theater organs which simulate the characteristic sound of a theater pipe organ, and institutional or classical organs which simulate pipe organs generally found in churches and concert halls. Although classical pipe organ literature is best played on a true pipe organ, such organs are very expensive and require frequent maintenance to maintain the pipes in tune. Furthermore, changes in humidity and temperature affect the operation and sound of the organ, and the number of technicians who can maintain and tune pipe organs is rapidly dwindling. Consequently, pipe organs have become so expensive that they are beyond the means of most musicians and many churches.
In order to permit classical literature to be played, electronic organs have been developed which simulate, to varying degrees of closeness, the sound of a pipe organ. One approach is to utilize a pure digital system wherein the sounds produced by the various instruments are digitally stored in memories which are then addressed at a variable rate depending on the keys depressed to produce the tones of the instruments at the frequencies desired. Systems of this type have unique problems which prevent them from being completely satisfactory, however. Firstly, the number of harmonics as a function of the frequency of the waveform varies somewhat because of the limited number of sample points at low frequencies, and, secondly, aliasing is a significant problem. Other organs of this type utilize pure analog techniques where individual tone generators produce the various voices, and complex switching arrangements are utilized to key the tones. The circuitry and switch arrangement for such an organ is extremely complex and unwieldy, however, and this greatly increases the physical size and cost of the organ as well as posing significant maintenance problems. The third approach, and that which is employed in the present system, it is to combine digital and analog techniques to utilize the advantages inherent in each of them.
In a pipe organ or an electronic organ simulating a pipe organ, the upper manual is referred to as the Swell manual because the volume level of those voices was traditionally controlled by a swell chamber having a series of shutters which opened and closed under the control of the organist. The lower manual is referred to as the Great manual, and it, like the Swell manual, comprises sixty-one keys. The pedal manual comprises thirty-two pedals arranged in a convex pattern. The voice controls are referred to as stops and take the form of rocker tabs, blade-type tabs or drawbars.
Such organs also include a particular type of special effect control known as couplers, both intermanual and intramanual. Intermanual couplers enable voices normally assigned to one manual, including the pedalboard, to be played on another manual. For example, the pedalboard can be caused to play voices assigned to certain ranks of the Great manual, or the Swell manual may be coupled to the Great manual and vice versa. Intramanual couplers, on the other hand, enable expansion of the basic rank of pipes. For example, if an eight foot flute voice is played on the Great manual, and the four foot Great to Great coupler is activated, the organ will produce both the eight foot flute and the four foot flute. Likewise, if the sixteen foot Great to Great coupler is actuated, the sixteen foot flute rank will also be played.
A technique which is often employed in pipe and electronic organs is referred to as unification, which permits more ranks of pipes or voices to be produced within duplicating each pipe or voice in the rank. For example, a rank of diapasons at the eight foot level requires sixty-one pipes, and in a non-unified system, to add a rank of four foot diapasons, in additional sixty-one pipes would be necessary, for a total of one hundred twenty-two pipes. However, of the five octaves of four foot diapasons, four of them are at the same pitch as the original eight foot rank diapasons, so that there are forty-eight redundant pipes. In a unified system, then, for each additional footage, only twelve pipes or keyers are added, so that for the combined two foot, four foot, eight foot and sixteen foot ranks, a total of only ninety-seven pipes or keyers are necessary. The disadvantage to this is that the chorus effect is not as pronounced, but this is offset by the very substantial cost savings.
A feature often included in institutional organs is a transposer, which permits the key of the instrument to be changed to match music which is being played together with the organ. For example, if a choir cannot easily sing the piece of music in the key that it is written, in the absence of a transposer, the organist would have to mentally transpose it by one or more half steps, which requires a very high degree of skill.
In electronic organs of the classical or institutional type in question, the large number of voices which are available for selection and the presence of couplers which enable each manual to be coupled to the other manuals and enables ranks to be coupled to each other within a manual renders the control of keydown and voicing data quite complex. In non-multiplexed organs, there are a large number of physical interconnections between the various manuals, keyswitches, couplers, stops, keyers and tone generators, all of which add to the cost of manufacturing and the difficulty and cost of repairing the organ and keeping it in tune. Although multiplexing greatly simplifies the inner connections from the manuals, the manner of handling the keydown data, particularly in the areas of intermanual and intramanual coupling and in the area of demultiplexing the data, has remained complex and unwieldy.
Pipe organs are capable of producing voices known as mixtures, which comprise two to five or more pitches produced simultaneously by depressing a single key. The pitches are generally unison and mutation pitches so that a 1 3/5 foot mixture comprises a 2 foot pitch, a 1 3/5 foot pitch, and a 1 foot pitch, for example. The ranking of the mixture on the keyboard determines the pitches that are played, so depending where on the manual the key is depressed, the mixture will comprise either two unison and one mutation pitches, as in the previous example, or two mutations and one unison pitch. In the latter case, the mixture would comprise, for example, a 11/3 foot pitch, a 2 foot pitch, and a 22/3 foot pitch.
In the past, the mixtures have been generated by keying the selected tones themselves. Although this enables the proper tones to be played, the switching arrangement is quite complex because it requires that different keyers be activated depending on the position in the manual of the depressed key or keys.